[CQ] bump to latest stable lints package dep (flutter#8153)

Keeping up with the Joneses.

---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide]([https://github.com/dart-lang/sdk/blob/main/CONTRIBUTING.md](https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview)
for general expectations for PRs.
- Larger or significant changes should be discussed in an issue before
creating a PR.
- Dart contributions to our repos should follow the [Dart style
guide](https://dart.dev/guides/language/effective-dart) and use `dart
format`.
- Java and Kotlin contributions should strive to follow Java and Kotlin
best practices
([discussion](flutter#8098)).
</details>

Author: pq

pubspec.yaml

@@ -15,5 +15,5 @@ dependencies:
 dev_dependencies:
   grinder: ^0.9.3
   http: ^1.2.0
-  lints: ^5.0.0
+  lints: ^6.0.0
   meta: any

tool/plugin/pubspec.yaml

@@ -16,5 +16,5 @@ dependencies:
   string_validator: 1.1.0
 
 dev_dependencies:
-  lints: ^5.0.0
+  lints: ^6.0.0
   test: ^1.22.0